Air Quality in Virginia

How clean is the air in your metropolitan area or county? Use this map to find out.

The U. S. Environmental Protection Agency (EPA) has provided a scale called the Air Quality Index (AQI) for rating air quality. The AQI scale is based on the National Ambient Air Quality Standards (NAAQS) and is described in the Code of Federal Regulations, Part 58, Appendix G. This map is based on the EPA AQI scale.

The latest AQI imagery available is for August 17, 2017 as of 10:45 pm EDT (Eastern Daylight Time).Click on any of the boxes on the image for a detailed map of all the sites monitoring AQI pollutants in that area.You can also view a tabular presentation of the Air Quality Index (AQI) Report for the entire state.

PLEASE NOTE: Data in this image is collected from Virginia DEQ air monitoring sites, local agencies, and private monitoring networks. This data has not been verified by the Virginia DEQ or the responsible entity and may change. While this is the most current data, it is not official until it has been certified by the appropriate technical staff. This image is updated hourly.

The image above shows the Air Quality Index (AQI) ratings for each of the NAAQS pollutants that are measured real-time and the critical pollutant that is driving the AQI rating in each metropolitan area, county or other area where pollutant levels are monitored by the Virginia DEQ. The critical pollutant is the pollutant with the highest AQI rating measured in the area. The image is updated each hour and covers the period from midnight through the indicated ending time.

Which Pollutants Can I Monitor Using the AQI?

There are five pollutants that go into the Air Quality Index: ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and particulate matter. In the image above, each monitoring area is represented by a small box which is color coded to match the AQI rating for the day (see Interpreting the AQI). Inside the box, the pollutant that is driving the AQI rating is identified by its abbreviation (see the table below). At the bottom of each box is a small legend that indicates which pollutants are actively measured in that area. Each of the smaller boxes is color coded to match the AQI rating for that specific parameter. Please note that not all pollutants are measured in all areas or at all sites. The table below briefly describes each pollutant that goes into the AQI.

Pollutant

Abbreviation

Description

Ozone

O3

Ozone is a form of oxygen with three atoms instead of the usual two atoms. It is a photochemical oxidant and, at ground level, is the main component of smog. Unlike other gaseous pollutants, ozone is not emitted directly into the atmosphere. Instead, it is created in the atmosphere by the action of sunlight on volatile organic compounds and nitrogen oxides.

Higher levels of ozone usually occur on sunny days with light winds, primarily from March through October. An ozone exceedance day is counted if the measured eight-hour average ozone concentration exceeds the standards.

Carbon Monoxide

CO

Carbon Monoxide (CO) is a colorless, odorless, very toxic gas produced by the incomplete combustion of carbon-containing fuels, most notably by gasoline powered engines, power plants, and wood fires. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.

Sulfur Dioxide

SO2

Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as "oxides of sulfur." The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse effects on the respiratory system.

Nitrogen Dioxide

NO2

Nitrogen dioxide (NO2) is one of a group of highly reactive gasses known as "oxides of nitrogen", or "nitrogen oxides (NOx)". Other nitrogen oxides include nitrous acid and nitric acid. While EPA's National Ambient Air Quality Standard covers this entire group of NOx, NO2 is the component of greatest interest and the indicator for the larger group of nitrogen oxides. NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.

Particulate Matter

PM-2.5PM-10

Particle pollution (also called particulate matter or PM) is the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small, they can only be detected using an electron microscope. Particle pollution includes inhalable coarse particles, with diameters larger than 2.5 micrometers and smaller than 10 micrometers and fine particles, with diameters that are 2.5 micrometers and smaller. How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter -- making it 30 times larger than the largest fine particle. These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some particles, known as primary particles, are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Others form in complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. These particles, known as secondary particles, make up most of the fine particle pollution in the country.

Interpreting the AQI

Each NAAQS pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration of the Federal Standard for that pollutant. Additional information about the AQI and how it can be used is available from the EPA's AirNow web site.

Place your mouse pointer over the scale displayed above to view information about the Air Quality Index, and each of the rating levels.

The actual index calculation is different for each parameter measured and is specified by the EPA. The following table shows the various breakpoints used in calculating the AQI.

AQI Breakpoint Definitions

AQI Range

1hr Ozonein ppm

8hr Ozonein ppm

8hr Carbon Monoxidein ppm

1hr Sulfur Dioxidein ppm

24hr Sulfur Dioxidein ppm

1hr Nitrogen Dioxidein ppm

24hr PM-10in µg/m³ (25° C)

24hr PM-2.5in µg/m³ LC

24hr PM-2.5in µg/m³ LC

0 - 50

Not Defined

0 - 0.054

0 - 4.4

0 - 0.035

Not Defined

0 - 0.053

0 - 54

0 - 12.0

0 - 12.0

51 - 100

Not Defined

0.055 - 0.070

4.5 - 9.4

0.036 - 0.075

Not Defined

0.054 - 0.1

55 - 154

12.1 - 35.4

12.1 - 35.4

101 - 150

0.125 - 0.164

0.071 - 0.085

9.5 - 12.4

0.076 - 0.185

Not Defined

0.101 - 0.36

155 - 254

35.5 - 55.4

35.5 - 55.4

151 - 200

0.165 - 0.204

0.086 - 0.105

12.5 - 15.4

0.186 - 0.304

Not Defined

0.361 - 0.649

255 - 354

55.5 - 150.4

55.5 - 150.4

201 - 300

0.205 - 0.404

0.106 - 0.200

15.5 - 30.4

Not Defined

0.305 - 0.604

0.65 - 1.249

355 - 424

150.5 - 250.4

150.5 - 250.4

301 - 400

0.405 - 0.504

Not Defined

30.5 - 40.4

Not Defined

0.605 - 0.804

1.25 - 1.649

425 - 504

250.5 - 350.4

250.5 - 350.4

401 - 500

0.505 - 0.604

Not Defined

40.5 - 50.4

Not Defined

0.805 - 1.004

1.65 - 2.049

505 - 604

350.5 - 500.4

350.5 - 500.4

500+

Not Defined

Not Defined

Not Defined

Not Defined

Not Defined

Not Defined

Not Defined

Not Defined

Not Defined

The AQI for ozone is based on either the peak eight-hour running average since midnight OR the peak one-hour measurement since midnight. When calculating air quality for the current day, the Virginia DEQ uses a surrogate 8-hour average based on the current hourly average.

The AQI for carbon monoxide is based on the peak eight-hour running average since midnight.

The AQI for sulfur dioxide is based on the peak one-hour measurement since midnight. There is a secondary NAAQS based on a 24-hour average of sulfur dioxide sampled from midnight to midnight, but this NAAQS has such a high starting point that is is never expected to be reached.

The AQI for nitrogen dioxide is based on the peak one-hour measurement since midnight.

The AQI for PM-10 is based on a 24-hour average sampled from midnight to midnight.

The AQI for PM-2.5 is based on a 24-hour average sampled from midnight to midnight.

The AQI for PM-2.5 is based on a 24-hour average sampled from midnight to midnight.

PLEASE NOTE: This data has not been verified by the Virginia DEQ and may change. This is the most current data, but it is not official until it has been certified by our technical staff. Data is collected from Virginia DEQ ambient monitoring sites and may include data collected by other outside agencies. This data is updated hourly. All times shown are in local standard time unless otherwise indicated.